March 2003

1

MICRF501

MICRF501

Micrel

MICRF501

300MHz to 600MHz RadioWire™ RF Transceiver

Final

General Description

The MICRF501 is a single chip tranceiver intended for ISM

(Industrial, Scientific and Medical) and SRD (Short Range

Device) frequency bands from 300MHz to 600MHz with FSK

data rates up to 128k baud.

The transmitter consists of a PLL frequency synthesizer and

a power amplifier. The frequency synthesizer consists of a

voltage-controlled oscillator (VCO), a crystal oscillator, dual-

modulus prescaler, programmable frequency dividers and a

phase-detector. The loop filter is external for flexibility and

can be a simple passive circuit. The VCO is a Colpitts

oscillator which requires an external resonator and varactor.

FSK modulation can be applied externally to the VCO or the

crystal oscillator. The synthesizer has two different N, M and

A frequency dividers. FSK modulation can also be imple-

mented by switching between these dividers (max. 2400bps).

The lengths of the N and M and A registers are 12, 10 and 6

bits respectively. For all types of FSK modulation, data is

entered at the DATAIXO pin (see application circuit). The

output power of the power amplifier can be programmed to

eight levels. A lock-detect circuit detects when the PLL is in

lock.

In receive mode the PLL synthesizer generates the local

oscillator (LO) signal. The N, M and A values that give the LO

frequency are stored in the N0, M0 and A0 registers. The

receiver is a zero intermediate frequency (IF) type in order to

make channel filtering possible with low-power integrated

low-pass filters. The receiver consists of a low noise amplifier

(LNA) that drives a quadrature mixer pair. The mixer outputs

feed two identical signal channels in phase quadrature. Each

channel includes a preamplifier, a third order Sallen-Key RC

low pass filter that protects the following gyrator filter from

strong adjacent channel signals and finally, a limiter. The

main channel filter is a gyrator capacitor implementation of a

seven-pole elliptic low pass filter. The elliptic filter minimizes

the total capacitance required for a given selectivity and

dynamic range. The cut-off frequency of the Sallen-Key RC

filter can be programmed to four different frequencies: 10kHz,

30kHz, 60kHz and 200kHz. An external resistor adjusts the

cut-off frequency of the gyrator filter. The demodulator de-

modulates the I and Q channel outputs and produces a digital

data output. It detects the relative phase of the I and the Q

channel signal. If the I channel signal lags the Q channel, the

FSK tone frequency lies above the LO frequency (data ‘1’). If

the I channel leads the Q channel, the FSK tone lies below the

LO frequency (data ‘0’). The output of the receiver is available

on the DATAIXO pin. A RSSI (Receive Signal Strength

Indicator) circuit indicates the received signal level.

Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com

Features

• Frequency range: 300MHz to 600MHz

• Modulation: FSK

• RF output power: 12dBm

• Maximum data rate: 128k bauds

Applications

• Telemetry

• Remote metering

• Wireless controller

• Wireless data repeaters

• Remote control systems

• Wireless modem

• Wireless security system

Ordering Information

Part Number

Ambient Temp. Range

Package

MICRF501BLQ

–40

°C to +85°C

44-Lead LQFP

RadioWire is a trademark of Micrel, Inc.

A two pin serial interface is used to program the circuit.

External components are necessary for RF input and output

impedance matching and decoupling of power. Other exter-

nal components are the VCO resonator circuit with varactor,

crystal, feedback capacitors and components for FSK modu-

lation with the VCO, loop filter, bias resistors for the power

amplifier and gyrator filters. A T/R switch can be implemented

with 2-pin diodes. This gives maximum input sensitivity and

transmit output power.

RadioWire™